1. Field of Invention
This invention relates to compositions and methods of reducing the breakup or spalling which occurs when a pavement is covered with either water or de-icing solutions produced from the action of a de-icing compound and then subjected to the destructive action of the freezing and thawing of these liquids--particularly when removal of snow or ice from pavement is sought.
2. Prior Art
The Operator, Snow Fighter's Handbook for the Utah State Department of Highways, gives the following description of a method for maintaining bare highways during snowfall: "Begin salt application when the ground is BARELY WHITE and it is wet enough to hold the salt on the roadbed. It is really important that the salt is applied at this time because you are doing more than just applying salt--you are forming a brine cushion to `float` the snow layer on. This brine has two purposes: 1--It melts snow from the pavement up so that snow and ice don't stick to it, and 2--It `greases` the snow layer so that the snow plows can push it off the road more completely than without it.
"On Type I service you apply straight salt at the rate of 0.25 cubic yards per 2 lane mile or salt-abrasive (1-1 salt-sand) mixture at 0.50 cubic yards per 2 lane mile. Let the salt sit (sic) one hour to develop a brine. Reapply every 6 hours during the storm when the storm lasts that long. Plow the road continuously every one and a half-hours--bare pavement maintenance."
If one quarter cubic yard of salt is estimated to weigh 450 pounds, if it is assumed that when the ground is "barely white" that there is 1/4inch of snow and if it is assumed that ten inches of snow is equivalent to one inch of water, the most concentrated brine that would be formed under the described highway practice would be about 2.7 percent by weight sodium chloride. This is also equivalent to 0.00355 pounds of salt per 0.1299 pounds of water per square foot of surface or 0.032 pounds of salt (1/18 cup or 0.45 volumetric ounces) per square yard.
In the February 1973 issue of "Consumer Reports" is found the following directions for keeping the snow off of a sidewalk: "The temperature is within a couple of degrees of freezing, wet snow is falling and the forecast is for a total accumulation of 2 inches: Spread rock salt or calcium chloride at about one cup per square yard to melt the snow as it falls or, shovel."
The Portland Cement Association published in 1968 the "Concrete Information" pamphlet titled "Effect of Various Substances on Concrete and Protective Treatments, Where Required." This pamphlet is a recognized source of information on the known affects that many chemicals have on concrete. With the exception of protective coatings, no mention is made in this pamphlet of any chemical which would protect concrete against the deleterious effects which either freezing and thawing or any chemical may have on concrete. In this pamphlet, the following is said of sodium and calcium chloride: "Frequently used as a de-icer for concrete pavements. If the concrete contains insufficient entrained air or has not been air dried for at least 30 days after completion of curing, repeated application may cause surface scaling."
Under the heading of Miscellaneous and of De-icers, the following statement is made: "Chlorides (calcium and sodium), urea and ethyl alcohol cause scaling of nonair-entrained concrete."
The following protective coatings are listed as treatments to prevent or reduce the damage to concrete from de-icers: "50% solution of boiled linseed oil in kerosene, soybean oil, modified castor oil, sand filled epoxy or coal-tar epoxy."
Volume 323 of the Highway Research Board Bulletin lists a test in which 2.4 pounds of de-icing salt was applied per square yard. (This is 75 times the recommended rate for highways.) In this test after 75 freeze-thaw cycles on air-entrained concrete that contained six percent entrained air, the calcium chloride had produced 41/2 times as much spalling as water and sodium chloride had produced 61/2 times as much spalling.